Abstract: The cracking gas compressor of an 800kt/a ethylene plant in China is large localized compressor unit with three cylinders and five stages, and is designed with three stages of backflow to one-stage suction, four stages of backflow to four-stage suction and five stages of backflow to five-stage suction to prevent the surge. In three years’ operation, there were problems including the operation safety margin of three-stage anti-surge system is low, the action of four-stage anti-surge valve easily leads to compressor trip, and the action of five-stage anti-surge valve easily leads to C2 front-end hydrogenation reactor trip. During the overhaul in 2016, the control system of the cracking gas compressor unit was optimized, the above-mentioned problems were solved successfully, the degree of automation was improved, energy saving and consumption reduction were achieved, and the operation of the compressor unit was stabilized.

Key words: ethylene plant}cracking gas compressor；anti-surge, optimization